I especially hate it when in 2vs2 matches are actually very close and entertaining while I am spectating it, like tied on and off constantly, but because of the one of the two people are raging because they got killed too many times because they can't jump in and pwn all they quit and leave the actual good team working player in a 2 on 1, then they just get raped usually. Which is quite annoying I think, I don't think the one good player on the team should suffer a lost just because of that player's lack of skill and team work.
Also, why I only do 2vs2's with friends of mine. So, I don't get bailed out on.